1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a capped contact plug.
2. Description of the Related Art
Generally, in semiconductor devices having multi wiring layers made of aluminum or its alloy, as integration has been developed, the width and spacing of the wiring layers have been reduced.
In a first prior art semiconductor device, a non-capped contact plug is provided between a lower wiring layer and an upper wiring layer. This will be explained later in detail.
In the above-described first prior art device, however, since the contact plug is non-capped, so that only an upper surface of the lower wiring layer is in contact with the contact plug, the contact area between the contact plug and the lower wiring layer is so small as to restrict the reduction of contact resistance of the contact plug.
Also, if a desired contact resistance of the contact plug cannot be obtained, the size of the contact plug needs to be larger. In this case, the pitch of lower wiring layers needs to be larger, thus inviting a reduction of the integration.
In a second prior art semiconductor device, in order to reduce the resistance of contact plugs without increasing the pitch of lower wiring layers, capped contact plugs have been known. This will also be explained later in detail.
In the above-described second prior art device, however, it is actually difficult to suppress the increase of resistance of the capped contact plug. At worst, the resistance of the capped contact plug is remarkbly increased. That is, an insulating layer including AlF.sub.3 is created between the capped contact plug and the lower wiring layer, which increases the contact resistance of the capped contact plug.